"Harry Potter" star Daniel Radcliffe has cast a spell on actress Erin Darke, his costar in the upcoming film "Kill Your Darlings." The two were seen packing on the PDA at Grey Goose Blue Door in Park City, Utah, on Friday, Jan. 18, sources confirm to Us Weekly.

"They were affectionate most of the night," says a source, who notes that Darke "was touching his knee" at their VIP table. "They were a little more obvious outside the venue after they were leaving."

The stars have yet to comment on the nature of their relationship, though a second insider says "they've been seeing each other" quietly in New York, where they both live. (Radcliffe's ex-girlfriends include production assistant Rosie Coker and actress Laura O'Toole.)

When Us caught up with Radcliffe, 23, at the Kill Your Darlings premiere Jan. 19, the English actor was strictly business. The film centers around a 1944 murder that brings together the Beat Generation's greatest poets: Allen Ginsberg (Radcliffe), Jack Kerouac (Jack Huston) and William Burroughs (Ben Foster). "It's an incredible story," Radcliffe said. "It's a pleasure to finally be able to tell it."

The role required Radcliffe to film his first gay sex scene -- a big departure for the man who played the world's most famous child wizard. Even so, Radcliffe still remains close with his Harry Potter costars Emma Watson and Rupert Grint.

"I think we're all kind of looking out for each other, and kind of eagerly waiting for each other's films to come out. We're definitely looking out for each other with a very positive eye," Radcliffe told Us. "I think so far we're all doing really well."